The average adult produces and in parallel eradicates 50-70 billion cells daily as a result of programmed cell death (apoptosis). Defects in apoptosis contribute to many human diseases, including cancer, where excessive cell accumulation due to failed programmed cell death is a common occurrence. Suppression of apoptosis contributes to carcinogenesis by several mechanisms, including prolonging cell life-span, thereby facilitating the accumulation of gene mutations;permitting growth factor-independent cell survival;promoting resistance to immune-based cytotoxicity;allowing disobeyance of cell cycle checkpoints which would normally induce apoptosis;and producing resistance to chemotherapy and radiation. This program project grant application addresses the mechanisms by which signal transduction pathways impinge on and regulate the core cellular machinery responsible for controlling apoptosis. The competitive renewal application brings together the talents of multiple co-investigators, who have strong track records of collaborative productivity and contribution to the field of apoptosis. Four projects and 2 cores are proposed, integrated around a central theme of understanding mechanisms of cell death regulation and dysregulation in normal and malignant cells. Among the questions under interrogation are: (1) Studies of the mechanisms by which TNF-family receptors generate signals that either inhibit or promote apoptosis, focusing on the involvement of TRAF-family proteins and both classical and alternative NFkappaB activation pathways (Ware;Ely);(2) Investigations of the mechanism of pro-apoptotic protein Daxx, including functional analysis of its interactions with Rel-B and regulation of genes encoding caspase-inhibitory proteins (Reed;Frisch);(3) Interrogation of the mechanism of caspase-8 activation, and it dual apoptotic and non-apoptotic functions in the context of signaling by Fas/TNF-family death receptors (Salvesen;Green);and (4) Elucidation of the mechanism by which pro-apoptotic proteins Bax and Bak alter mitochondria membrane permeability (Green;Newmeyer;Hanein;Volkman). Together, the cross-fertilization of ideas that emerges from these related projects will provide mechanistic insights into normal and aberrant apoptosis regulation, laying a foundation for future advances in the treatment of cancer and other diseases.